Non-reciprocal directional filter



Feb. 4, 1969 M. COHEN NON-REGIPROCAL DIRECTIONAL FILTER Filed Feb, 25. 1966 ROTATABL E ROD YIG SPHERE United States Patent 3,426,297 NON-RECIPROCAL DIRECTIONAL FILTER Morris Cohen, Oceanside, N.Y., assignor to Loral Corporation, Bronx, N.Y. Filed Feb. 25, 1966, Ser. No. 538,134 US. Cl. 333--1.1 Int. Cl. H01p 1/32; H03h 7/10 3 Claims ABSTRACT OF THE DISCLOSURE This invention relates generally to the field of radio frequency transmission, and more particularly to an improved electronically tuned twoand four-port non-reciprocal directional filters employing a sphere of gyromagnetic material as a tunable element.

It is among the principal objects of the present invention to provide a two-port or four-port electronically tunable non-reciprocal band rejection filter suitable for operation with coaxial type or strip transmission lines.

Another object of the invention lies in the provision of an improved band rejection filter of the class described which may be readily and simply constructed using a coaxial or strip transmission line having a right angle bend.

Another object of the invention lies in the provision of an improved filter structure particularly suited for operation in the X-band region of frequency, although having application in lower frequency regions as well.

These objects, as well as other incidental ends and advantages, will more fully appear in the progress of the following disclosure, and be pointed out in the appended claims.

In the drawing, to which reference will be made in the specification, similar reference characters have been employed to designate corresponding parts throughout the several views.

FIGURE 1 is a view in perspective showing a first embodiment of the invention.

FIGURE 2 is a fragmentary longitudinal sectional view of the first embodiment, and showing schematically the direction of certain magnetic fields involved in the operation of the device.

FIGURE 3 is a schematic end elevational view as seen from the lower portion of FIGURE 2.

FIGURE 4 is an exploded view in perspective showing a second embodiment of the invention.

FIGURE 5 is a view in perspective of the second embodiment in fully assembled condition.

In accordance with the first embodiment of the invention, the device, generally indicated by reference character 10, includes a right angle coaxial conductor having first and second legs 11 and 12, respectively, and including an outer conductor 13 and an inner conductor 14, as is well known in the art. It will be understood that the use of the term coaxial conductor is intended to include equivalent structures such as strip line conductors operating in the TEM mode, but excluding such devices as wave guides which do not have.an inner conductor.

Referring to FIGURE 2, a YIG sphere 22 is supported on the end of a dielectric rod 23 which penetrates the outer conductor 13 at the interconnection of the first and 3,426,297 Patented Feb. 4, 1969 second legs 11 and 12. The rod is rotatable about its own axis for purposes of tuning, and locates the sphere 22 in the approximate center of the interstice formed between the inner and outer conductors.

Operation of the device 10 will be more clearly understood from a consideration of FIGURES 2 and 3. A necessary requirement for nonreciprocity is that the microwave magnetic field in the region of the YIG sphere be circularly polarized. While this requirement is easily met in rectangular and cylindrical wave guides, in the coaxial or strip transmission line propagating the TEM mode, the microwave magnetic field is linearly polarized at all points, and hence, any ferrite effects will be completely reciprocal.

With reference to FIGURE 2, in the regions indicated by reference characters A and C, the magnetic field is linearly polarized. However, in the bend region B, the magnetic field is distorted and may be resolved into two components, Hx and Hy, equal in amplitude and degrees in phase quadrature, yielding the necessary conditions for circular polarization, and hence, non-reciprocal operation. The sense of the circularly polarized field will depend upon the direction of propagation of the TEM wave, as indicated by reference character 16 in FIG- URE 3.

With the YIG sphere 22 located as shown in FIGURE 2, resonance is achieved by an externally applied magnetic field which is applied orthogonally to the Hx and Hy field components. When the precession direction (controlled by the direction of the external field) is in the same sense as the circularly polarized field, the energy is transferred to the YIG sphere 22 and very little output appears at the output port 18, thus obtaining band rejection. However, when energy is fed into port 18, the circularly polarized wave will be opposite to the precession direction, and will not be transferred to the YIG sphere, hence substantially all of the energy appears at port 17, thus achieving non-reciprocity.

In order to ascertain the validity of the theory discussed hereinabove, an experiment was conducted using a cylindrical right angle bend coaxial connector, and a 50 mil YIG sphere having a linewidth equal to 0.9 oersted. A biasing external magnetic field was supplied by a Varian magnet. This structure was tested over a frequency range between 10.0 and 12.0 go. with the following observed results:

(a) H direction assumed (1) Band rejection notch 20-30 (2) Passband insertion loss 0.5

(b) H direction opposite that first assumed (1) Band rejection notch 1.0- 0.5

(2) Passband insertion loss 05 It is evident that the directivity of the tested device varied from 19.0 to 29.5 db over the frequency range of 10.0 to 12.0 gc. respectively.

Turning now to the second embodiment illustrated in FIGURES 4 and 5 in the drawing, the device, generally indicated by reference character 25 is in the form of a TEM non-reciprocal directional preselector. It includes first and second right angle coaxial conductors 26 and 27, respectively which are interconnected in angularly oppositely disposed orientation by a coupling iris 28 supporting a YIG sphere 29 on a mounting rod 30'.

The conductors 26 and 27 are similar, each including first and second legs 32 and 33, the outer conductors being of rectangular cross-section to include sides 34, 35, 36 and 37. The internal conductor 38 is centrally disposed within the rectangular cross-section formed thereby. Dis- 3 posed at the apex angle of each conductor is a rectangular opening 39 formed by edges 40, 41, 42, 43, 44 and 45.

The coupling iris 28 is in the form of a metal plate 50 having planar surfaces 49, and side surfaces 51, 52 corresponding in dimensions such that the iris nests in the openings 39 when the device is assembled as shown in FIGURE 5.

During operation, when the YIG sphere is not resonant, power entering port 60 does not couple through the iris, but instead goes directly to a matched load or matched detector at port 61. When the YIG sphere is resonated by an external magnetic field, power entering port 60 is coupled through the YIG sphere to port 62, and any reflections from port 62 do not couple back to port 60, due to non-reciprocity but instead go to port 63. If port 62 is matched, port 63 is decoupled. In order to reverse the operation, the direction of the external magnetic field must be reversed.

It may be seen that I have invented a novel and highly useful construction for achieving non-reciprocity in a two conductor line operating in the TEM mode. The validity of the theory of operation is verified by experimental data. The structure may be used, if desired, with tunnel diode amplifiers and acts as both the tuning and circulator mechanisms, or may be used as a chain of channel dropping filters, that is to say multiplexing.

I wish it to be understood that I do not consider the invention limited to the precise details of structure shown and set forth in this specification, for obvious modifications will occur to those skilled in the art to which the invention pertains.

I claim:

1. An electronically tunable two port non-reciprocal band rejection filter comprising: a coaxial conductor having first and second conductor members disposed at substantially a right angle in a plane, said coaxial conductor having a first outer conductor member and a second inner conductor member disposed therewithin in parallel relation, and being free of interconnection with said outer conductor member, a sphere of gyromagnetic material supported within the said coaxial conductor in proximity to said inner conductor member substantially at the apex of the said angle, rod means supporting said sphere for rotation about the axis of said rod, and means for supplying a DC magnetic field to said sphere.

2. An electronically tunable four port non-reciprocal directional microwave preselector comprising: a first c0- axial conductor having first and second interconnected legs disposed at substantially a right angle and lying in a first plane, said coaxial conductor including a hollow outer conductor member and an inner conductor member disposed therewithin in parallel relation, and being free of interconnection with said outer conductor member; a second coaxial conductor having third and fourth interconnected legs disposed at substantially a right angle and lying in a second plane parallel to said first plane, said second coaxial conductor including a hollow outer conductor member and an inner conductor member disposed therein in parallel relation, and being free of interconnection with said outer conductor member; the outer conductor member of each of said first and second coaxial conductors being in mutual communication with said inner conductors placed in juxtaposed position in the area of interconnection of said legs of each of said conductors; a sphere of gyromagnetic material supported in the interstice between said juxtaposed interconductor's; and means for providing a DC magnetic field to said sphere.

3. Structure in accordance with claim 2, in which said sphere is supported within an orificed coupling iris.

References Cited UNlTED STATES PATENTS 3,162,826 12/ 1964 Engelbrecht 333--24.2 X 3,274,519 9/1966 Nathanson 3331.1 3,289,112 11/1966 Brown 333--24.2 3,356,967 12/ 1967 Honig 33324.2

OTHER REFERENCES Lax and Button, Microwave Ferrites and Ferrimagnetics, McGraw-Hill, New York, 1962, pp. 466, 467 relied on.

=ELI LIEBERMAN, Primary Examiner.

P. L. GENSLER, Assistant Examiner.

US. Cl. X.R. 33373, 76 

